1. Field of the Invention
The invention relates to a method and a device for shaping the injection pressure course in injectors. Injectors and injection systems in which the injectors are used are employed to supply fuel to internal combustion engines of motor vehicles.
2. Prior Art
In the procedure of the prior art, in order to vary the course of the injection pressure during the injection, the volume of fuel positively displaced by the pump piston in the pump part of an injector housing is in part blown out via a slightly open control valve. Without the opening of the control valve, a continuous increase in the injection pressure would occur. This procedure is known by the abbreviation CCRS (for Current Controlled Rate Shaping), in which magnet valves, in particular, are used as units that actuate the control valves.
In another embodiment representing the prior art, a magnet valve is provided which serves the purpose of pressure buildup, along with a further pressure valve, which as a valve to be located downstream serves solely to regulate the pressure level during the pressure buildup phase (boot phase).
With the embodiments of the prior art, only individual phases of the injection pressure course can be regulated during the injection. A more-extensive shaping of the injection pressure course, along with a substantially more-compact structural shape of injectors, is not possible since the embodiments described here use magnet valves that take up space on the one hand and on the other need further magnet valves in order to shape the injection pressure course in more detail.
With the method and the device proposed according to the invention, both the duration of the preinjection phase and the duration of the pressure buildup phase can be determined by the triggering by means of an actuator. Furthermore, with the method proposed, specifying the pressure to various pressure level values during the pressure buildup phase is possible. The same is analogously true for setting the height of the allowable and mechanical still tolerable maximum pressure toward the end of the main injection phase. Depending on the load-bearing capacity of the mechanical components, a pressure limitation toward the end of the main injection phase can be adapted to the applicable conditions of use of the injection system. It is furthermore possible with the method proposed according to the invention to assure that a diversion rate adapted variably to given conditions of use can be set. Depending on the intended use, the course of the pressure reduction can be preselected such that the instant of the end of the main injection and the instant of the onset of the pressure reduction phase can each be adapted individually.
With the method proposed according to the invention, the pump part of an injector system can be designed such that merely a single pump can be used for various designs of internal combustion engines. The pressure buildup phase for instance, which directly follows the preinjection phase, can be initiated by an actuator control in accordance with the intended use, regardless of how the nozzles and pump pistons are designed.
The course of the pressure in the pressure buildup phase is also independent of the load and the torque in the instantaneous operating state of the engine and can for instance be preselected precisely such that the pressure in the pressure buildup phase is just above the opening pressure for the nozzle needle received movably in the injector housing.
Another advantage attainable by means of the method of the invention is that the control valves can be moved into the sealing seat for the pressure buildup phase. As a result, it is possible to expand the actuator stroke tolerances, which makes the production of the actuator less expensive, since the protection against leakage losses for fuel that is at high pressure is assured by means of the control valves that have moved into their sealing position.
Triggering the control valves by means of a piezoelectric actuator makes it possible to dispense with magnet valves which take up greater space, and as a result the injector can be designed with an extremely compact construction.